The present invention relates generally to a direct drive transmission in which multiple power paths are used to divide and transmit input power to an output, and, more particularly, such a transmission in which helical gears interconnect such power paths in a manner which results in a balancing of loads on such power paths.
1. Field of the Invention
The power transmission industry is constantly seeking ways to transmit large loads through dimensionally small systems. However, in the absence of the use of exotic, high cost alloys, the design and construction of direct drive transmissions are often predetermined as to size by virtue of the particular application, loads transmitted, and cost. Accordingly, a given transmission is inevitably limited as to the load they can effectively transmit for any particular application. Larger loads typically entail larger gears, and if, e.g., a transmission is to be positioned in a well casing, its size is predetermined by its environment, and its capacity to deliver a required load to a driven element such as a pump, is likewise limited.
It is recognized that one way to reduce the overall size of the transmission is to divide, or split, the load carrying capacity of any given system into multiple paths defined by smaller load carrying elements, which would then permit a reduction in the size of the gears needed per element to transmit a design load. Then, by select spacing and positioning of the elements, the overall size of the spacing transmission is capable of being reduced.
It is equally recognized, however, that when multiple load carrying elements are receiving power from an input source for delivery to an output, whether it be in a step up or step down mode, there is an opportunity, indeed, likelihood, for imbalance between such load carrying elements.
Any such imbalance tends to accentuate wear and create an imbalance at the output end, even creating damaging harmonics, all of which greatly accelerate maintenance costs, and consequent down time, which tends to compromise, if not utterly defeat, the value of dividing the input power.
In summary, it will be appreciated that an unbalanced application of power, wherever it may occur in a transmission, inevitably results in uneven wear in the gearing and cyclic, or otherwise erratic, power output which, if not quickly ameliorated, will exacerbate the damage to the transmission itself, as well as any equipment to which it is drivingly connected.
2. Overview of the Prior Art
The concerns addressed by the present invention are not particularly new, although the solution offered herein is believed novel. Others have attempted to formulate a solution, including Mr. Morrow in his recently issued U.S. Pat. No. 5,927,147, which addresses and successfully resolves, gear loading problems in a single path gear train configuration. Schmitter (U.S. Pat. No. 2,654,267) utilized the power sharing ability of the dual helical gearing arrangement to allow a dual path drive with balanced load. That is, power input at gear 11 is split between intermediate pinions 15 and 16, which drive via dual bevel gears, and intermediate driven helical gears 39 and 40, which drive output helical pinions 45 and 46. Output pinions 45 and 46 have opposite helical angles and are mounted on an output shaft 47 which has limited axial movement. Axial movement of the output shaft is intended to provide balanced loading to the driven element connected thereto.
In a similar operating arrangement, Wallgren (U.S. Pat. No. 2,982,144) utilizes the characteristics of dual helical gearing wherein the driving dual helical gear pair is mounted on a drive shaft for limited axial movement to achieve balance load between two intermediate pinion shafts driving a single output gear.
In Whateley (U.S. Pat. No. 4,065,981) axially aligned input and output shafts are connected by helical gearing on intermediate shafts, and a dual helical arrangement on the output shaft is mounted for axial movement to provide balanced power to the output shaft.
Chung (U.S. Pat. No. 4,056,018) suggests a variation on the theme by providing additional intermediate shafts, 88 and 88xe2x80x2, equipped with dual helical pinions, 94 and 94xe2x80x2, that further drive four intermediate shafts, 96, 96xe2x80x2, 98 and 98xe2x80x2, finally driving a single driven pinion 30 via gears 108, 108xe2x80x2, 110, and 110xe2x80x2.
While there is prior art, each offering a variation directed to balancing loads on gears via the use of the load sharing characteristics of a dual helical gear set mounted on a shaft with limited axial movement, all share two serious limitations. A dual helical arrangement allows only one gear mesh for each of the two driven pinions, thereby limiting the input or output to that specific load capable of being transmitted by one gear. Since the drive pinions are single helical cut gears, a thrust load will be transmitted to the pinion shaft whenever load is carried by the pinion. This thrust load must be accommodated by the added expense of providing thrust bearing of some nature.
As will become apparent from a further reading of the following detailed description of a preferred embodiment, it will be appreciated that the invention taught herein represents a significantly and uniquely different approach to accomplishing load distribution in direct drive transmissions which are relatively small in size, yet capable to transmitting relatively large loads.
Having explored the environment in which the present invention has particular, although perhaps not exclusive, utility, it will now be appreciated that the geared transmission of the type addressed herein comprises, in one form, one or more pairs of helical gear sets, typically on parallel shafts, in operative engagement with a power input source and capable of delivering relatively great power therefrom, relative to its physical size, in a uniform balanced manner to the transmission output.
Clearly, therefore, a principal objective of the present invention is to provide a transmission of the type having a power input and pairs of intermediate elements engaging the input to split the power therefrom and deliver that power in a uniform and balanced manner to the transmission output.
A further objective incident to the foregoing, is to provide such a transmission which can deliver significant power from a single source to a driven member in an efficient and economical manner with minimal wear and tear on relatively standard, as distinguished from exotic, components which define the transmission and to accomplish this in a package which is smaller than would otherwise be anticipated, given the load parameters.
Another objective is to provide a transmission of the type having a power input and pairs of intermediate elements engaging the input to uniformly split the power, while providing much greater load capacity than heretofore possible.
A still further objective is to provide such a transmission wherein, during the transmission of power, all thrust loads on all gears, pinions and shafts are balanced. While the foregoing delineates several significant and practical objectives attainable by the structure of the invention, no effort has been made to articulate all of the objectives that are met by the gear set of the present invention, and others will become apparent to those skilled in the art as the forthcoming description of a preferred embodiment is studied, in conjunction with the appended drawings, wherein: